This invention relates generally to methods for controlled release of injected drugs and more specifically to controlled release vaccinations, which extend the duration of action of injected drugs or the duration of triggering of the immune response long after infection by slowly releasing the drug or vaccine into the circulatory system.
Currently, vaccinations include the need for multiple injections over time in order to generate a protective memory immune response. Because the immune system responds only modestly to initial contact with antigens, repeat injections are necessary. Immunity is an adaptive or learned process in which each subsequent exposure to antigen elicits a stronger antibody response. The response is stronger, not only in the quantity of antibody made but also in the average affinity (the strength of attachment or binding of the antibody for the antigen.) Affinity increases because only those B cells which possess high-affinity receptors are selectively triggered to proliferation and survival in the later stages of the immune response as the concentration of antigen falls. Early after injection, of course, the concentration of antigen is high enough to trigger both high and low affinity receptors. With repeated antigen injections, a greater number of the specific antibody forming B lymphocytes are produced by this enhanced proliferation and survival as xe2x80x9cmemoryxe2x80x9d cells and the quantity of antibody therefore increases.
Typically, a childhood vaccination protocol for diphtheria, tetanus and pertussis (DTP) requires a priming dose of vaccine at 2 months of age, a first booster injection at 4 months of age, a second booster at 6 months of age another dose at 15-18 months, and a recommended final dose at 4-6 years of age (Centers for Disease Control and Prevention, National Immunization Program.) Other vaccines require similar protocols. These vaccine injections cause pain and distress, especially in infants; therefore, child-care providers often fail to return with the children for later injections. As a result, the immunization protocol is compromised and children are not properly protected against disease. The World Health Organization (WHO) identified this failure of compliance as a widespread occurrence resulting in jeopardising mass immunization campaigns. (Jodar L., Aguado T., Lloyd J. and Lambert P-H (1998) Revolutionizing Immunizations Gen. Eng. News 18 p. 6.)
In order to address this problem, considerable efforts have been made to develop techniques which reduce the number of injections required. One approach is controlled release vaccines, which extend the duration of triggering the immune response long after each injection, by slowly releasing the vaccine into the circulation. Most of the work to date addresses the tetanus vaccine encapsulated in bio-erodible plastic micro-spheres of poly lactide/glycoloide polymers [(Xing D. K. L., McLellan K., Corbel M. J., and Sesardic D. (1996) Estimation of antigenic tetanus toxoid extracted from biodegradable microspheres. Biologicals 24, 57-65.] The biodegradable plastics slowly solubilize in body fluids thereby releasing vaccine gradually from the eroded hydrophobic particles after injection. However, the vaccines were found to be unstable in the body, therefore, early results were disappointing, but newer formulations overcame these problems and tetanus vaccine now works reasonably well in this system. Other fragile vaccines, however, are not stable in plastic particles in the body at 37xc2x0 C. It is for this reason that no other controlled release vaccine is currently in use.
In the course of developing stable liquids for injection, [(U.S. patent application Ser. No. 09/271,204 Composition and method for stable injectable liquids] stabilized formulations of tetanus vaccine in soluble, sugar glass microspheres suspended in anhydrous oils or perfluorocarbon liquids were studied. The stabilizing agent used was a soluble glass of the sugar alcohol mannitol which, upon contact with body water, it was expected to dissolve immediately and release its vaccine as a conventional priming dose. In pre-clinical testing, the stable liquid formulations were injected subcutaneously into groups of 10 guinea pigs. Dried vaccine was tested soon after manufacture (FIG. 1) and after it had been tested for stability by 3 months of accelerated aging at 37xc2x0 C. (FIG. 2).
Aliquots of dry vaccine, stabilized in sugar glass, were dissolved in water before injection and served as controls as well as fresh source vaccine as the standard biological control vaccine preparation. Antibody responses were measured at 4, 8, and 12 weeks after injection.
It was found that all the control vaccines produced the typical kinetic response of antibody titer after a priming dose, specifically, the antibody levels peaked at 4-8 weeks and then fell by 12 weeks. However, when both groups were injected with stabilized vaccine in glass microspheres suspended in anhydrous biocompatible liquids, the antibody levels in these animals continued to rise throughout the whole of the 12 weeks after injection. This result, not seen before in guinea pig tetanus toxoid immunization indicated a distinct change in the kinetics of antibody production. When compared with the historical results of antibody kinetics studies in guinea pigs infected with repeated doses of standard vaccine, the present studies indicated controlled release of antigen. The rising antibody levels seen in the present study at 12 weeks indicated protection of the animals equivalent to that seen after a multiple infection course of standard soluble vaccine.
While sugar glasses have proven to be efficacious in providing a stable milieu for fragile biological molecules, other water-soluble glasses such as the metal carboxylates and similar glasses (Slow Release Vitreous Systems PCT No. WO 90/11756) and the phosphate glasses (Phosphate Glass Ceramics for Biological na Medical Applications U.S. Pat. No 4,698,318) can also be formulated as glass microspheres, either in combination with sugar glasses or separately (Amorphous glasses for stabilizing sensitive products. PCT application WO 99/47174) and have other desirable properties which suit them for use in this system. This includes the ability to pre-determine the rate at which the glass dissolves by formulating it from a mixture of salts with individually different solubility rates in water (Controlled Delivery Devices U.S. Pat. No. 5,270,048).
The stable liquid formulations in anhydrous biocompatible liquids were initially developed to solve two major problems, namely the need to refrigerate drugs or vaccines for storage and the need to reconstitute them in the field with sterile water before injection. Not only does the technology clearly overcome these drawbacks, it appears that these formulations in anhydrous liquids also solve the compliance problem. A convenient/ready-to-inject, stable vaccine provides a complete course of immunization with a single injection in the present invention.
It is hypothesized that some of the soluble glass microspheres containing the stabilized vaccine are protected against dissolution in body water by remaining surrounded by anhydrous liquid. They dissolve only at some time after injection to release their vaccine, which then acts as a booster dose giving rising levels of antibody throughout the whole 12 weeks of the experiment.
A lower average antibody level at 4 weeks exists with anhydrous liquid preparations than with soluble antigen. This lower early titer in the groups given anhydrous liquid suspensions of vaccine is arguably the result of a lower dose of antigen being released soon after injection. Some may argue this indicates a problem of delayed onset of immunity, however the protective level of antibody in this system is approximately 0.1 international units per milliliter of blood. The levels seen in the guinea pigs at 4 weeks were more than 1 international unit per milliliter, well above the protective level even at such an early stage.
The present invention is a composition and method for controlled-release injections using soluble glass microspheres suspended in anhydrous liquids such as oils, silicone fluids or perfluorocarbons where a slow, controlled dissolution of the microspheres and release of antigen occurs over a considerable period of time after injection.
For a better understanding o f the present invention, together with other and further objects thereof, reference is made to the following description, taken in conjunction with the accompanying drawings, and its scope will be pointed out in the appending claims.